COMPARATIVE EFFICACY OF LEVAMISOLE, THIABENDAZOLE AND FENBENDAZOLE AGAINST CATTLE GASTROINTESTINAL NEMATODES

Efficacy of two older anthelmintics, levamisole and thiabendazole, was compared with a newer benzimidazole, fenbendazole, against naturally acquired gastrointestinal nematode infections in cattle superimposed w ith experimental infections of Bunostomum phlebotomum and Dictyocaulus viviparus. Twenty-four crossbred beef heifers of 7-9 months of age an d 152 kg in average weight were randomly allocated to four groups of s ix calves. The cattle grazed on pastures contaminated with larvae of g astrointestinal nematodes and the lungworm for 2 months prior to Day 0 . Treatment groups were as follows: Group 1-levamisole, topical at 10 mg kg(-1); Group 2-thiabendazole paste at 110 mg kg(-1); Group 3-fenbe ndazole paste at 10 mg kg(-1); Group 4-untreated controls. All calves were necropsied for worm recovery between 8 and 10 days after treatmen t. Fecal egg/larval per gram counts at 18 and 42 h post-treatment indi cated greatest reductions in Groups 1 and 2. By 7 days post-treatment, reduction in counts for all treated groups ranged from 99.1 to 100%, except for the 66.7% reduction of B. phlebotomum in Group 2. Seven nem atode species were present in a sufficient number of untreated control s for valid efficacy assessment at necropsy. Efficacy of fenbendazole was 100% against all species, including Cooperia spp. L(4) and immatur e (E5) D. viviparus. The overall efficacy of levamisole and thiabendaz ole was generally high (93.0-100% against Haemonchus placei adults, Co operia punctata and C. spatulata adult males, Cooperia spp. adult fema les, Oesophogastomum radiatum, B. phlebotomum, and D. viviparus adults ). Efficacy of levamisole was slightly better than that of thiabendazo le, although group mean differences for Ostertagia ostertagi adults, C ooperia spp. L(4), B. phlebotomum adults and D. viviparus E5 were not significant (P<0.05).